Veteran U.S. Sen. John McCain will announce Tuesday that he will seek a sixth term in 2016.

McCain, R-Ariz., plans to officially declare his bid for re-election during a speech before the Arizona Chamber of Commerce and Industry at the Arizona Biltmore resort in central Phoenix.

"The reason why I want to seek re-election is that there's a lot more to do, both for Arizona and the country," McCain told The Arizona Republic during a late Monday afternoon interview in his Phoenix office.

McCain, the 2008 Republican presidential nominee and chairman of the influential Senate Armed Services Committee, for months has indicated that he was strongly leaning toward running again, but he no longer is leaving any room for doubt.

Facing a possible GOP primary challenge by "tea party" conservatives, McCain insists that he will be prepared for any opponent who might try to take him on. The fundraising quarter that concluded March 31 found him with $3.5 million on hand, which is "a good beginning," he said.

"I think the reason why I have been successful is by not taking anything for granted, and by anticipating the worst and hoping for the best," McCain said. "But you've got to be ready."

McCain said his campaign will emphasize the state issues of "fire and water" and highlight his work on U.S. Department of Veterans Affairs reform, on the jobs-creating Resolution Copper mine legislation and on saving the A-10 Thunderbolt II, or "Warthog," whose pilots train at Davis-Monthan Air Force Base in southern Arizona.

He also believes his years of experience in national security will give him an edge at a time when the Middle East and Ukraine are in crisis.

"Being Armed Services Committee chairman, I've never seen the world in more turmoil," McCain said. "This president's feckless foreign policy has put us in a situation where we are in serious danger."

McCain, 78, would turn 80 before Election Day in 2016. He shrugged off questions about his age, saying his health "is excellent" and noting that his mother is 103 years old and "doing fine."

"Everybody makes their own judgment, but I would be glad to show somebody my daily schedule, both here and in Washington," McCain said. "I am more busy because of the chairmanship than I have ever been, except when I ran for president."

As McCain pursues re-election, he continues to face hostility from many conservative activists in the Arizona Republican Party. McCain was formally censured as too liberal in 2014, and during a January appearance before the state GOP, he faced a noisy mix of boos and cheers.

The major national tea-party-aligned conservative groups have indicated that they are watching the 2016 Senate race and may intervene against McCain if what they consider a viable conservative challenger emerges.

State Sen. Kelli Ward, R-Lake Havasu City, is the potential candidate who so far seems most serious about possibly running against McCain in the primary.

"It's my job to convince the voters, both primary and general, that I can do more for Arizona and the country, and I think I have a record to prove it," McCain said.